There are many great colleges that develop great talent. It depends on which college.
That said, Professional Baseball is by far the best developmental system. If for no other reasons (and there are other reasons)
1. It provides the best competition.
2. Coaches and Instructors are all professionals.
3. It's baseball only (every day) no studying chemistry or other tough classes to take up the time.
4. Longer season, more games
5. Adjusting to the life style, crowds, travel, media, etc.
That said, the college route is best for most players. It provides other areas of development that are even more important in life than baseball.
And as said before, going to college can really make some players much more attractive in the draft.